Mickey Karram led the peer-review process as the Associate Editor responsible for the paper.

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Conflict of interest: none.

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Authors' contributions: JB conceived, designed and coordinated the study, contributed to data collection, analysis and interpretation, prepared the manuscript; LP conceived and designed the study, contributed to data collection, analysis, interpretation and manuscript preparation; DR collected data, performed the statistical analysis, interpreted findings and helped prepare the manuscript; CM collected data and contributed to interpretation and manuscript preparation. All authors read and approved the final manuscript.